In recent days, men with earpieces have closely monitored passengers boarding Google commuter buses at the site of at least one bus stop in San Francisco's Mission District. Their presence comes a few weeks after Google buses were targeted by protesters who blame tech-industry employees for rising city rents.

Gone are the days when mentioning Google as an employer gave young technology workers a certain counterculture credibility. As the company has expanded well beyond its Web search-engine roots to become a behemoth encompassing advertising, smartphones, finance and social networking, it has gone from scrappy start-up to a Goliath that many resent for its power.

In San Francisco, many long-time residents believe the influx of richly compensated workers at Google and other big technology companies such as Facebook Inc and Twitter Inc has pushed rents to unaffordable levels in neighborhoods that once were homes to the working class.

Technology companies have grown more aware of the tensions. They recently reached an agreement with the city of San Francisco governing the use of municipal bus stops. Google recently began to experiment with a privately chartered boat that can transport some of its employees living in San Francisco to its offices.

And Google may be taking extra steps to protect its workers at the bus stops it uses in San Francisco.

A Google spokeswoman declined to comment.

On two successive days this week, a pair of young men stood on a San Francisco street waiting for the special "Gbus" that ferries Google staffers to the Internet company's Mountain View headquarters 34 miles to the South.

Dressed casually in jeans and wearing black ski hats or hoods, the two men did not stand out from the dozens of other young tech workers waiting for the Google bus. On close inspection, each sported the curly wire of an earpiece, and one occasionally jotted notes down on a yellow stick-it pad.

Instead of boarding the bus with everyone else, the two remained in the same spot, watching intently as a succession of Google's white corporate shuttles arrived for the morning pick-ups. In one instance, the bus driver waved to one of the men, who waved back.

Asked if they were security guards for Google buses, one of the men replied "Can I see your badge?" likely referring to the Google identification badges that employees of the company use to board the bus and enter buildings on the Google campus. The other man denied working as a security guard for Google, but declined to provide any information about his identity or his employer.

A Google employee who commutes on the buses said he does not recall previously seeing any type of monitoring at the bus stops.

In December, the window of a Google bus in Oakland was shattered and a photo taken by one of Google's employee passengers showed two people in front of the bus holding a profane anti-Google banner.

Other protests have been peaceful but disruptive, with activists temporarily blocking the corporate buses. One other Google bus in Oakland was targeted in December, plus a third bus at the same stop where the men with earpieces were observed this week.

Another commuter bus, believed to be taking employees to Apple Inc, was also targeted in December.

"They're bound to take steps to protect their workers," said Mike Danko, a personal injury lawyer in San Mateo, Calif., a San Francisco suburb.

"What would escalate the matter is any kind of violence," he said. "Usually the presence of a security person is going to keep a lid on violent conflict."

Ron Roth, the executive director of private security firm Corporate Security Service Inc said he did not know which security firm is working with Google.

"If they are having security at the bus stops it's probably only eyes and ears, and to act as liaison to the police, and probably not to take any action," said Roth.

While private security officers can be armed in California, providing they have the proper licenses, Roth said it was highly unlikely that anyone working on the bus detail would be armed.

"As a security company you really take on a liability if your officers are armed," he said.